'Superbull' males: what role do they play and what drives their appearance within the Doryteuthis gahi Patagonian Shelf population?

Abstract

Cephalopod populations exhibit high variability in life history characteristics, such as longevity and size-at-age. The aim of this study was to understand how characteristics of a newly described ‘superbull’ male morph in Doryteuthis gahi populations (Patagonian Shelf) arise and whether there is a selective advantage. At the population level, it is speculated that superbulls provide temporal and spatial connectivity, but individual benefit is less obvious. Age structure and reproductive potential of males was investigated to determine whether superbulls could provide connectivity. Environmental variables affecting size-at-age were explored to ascertain whether morphological differences were primarily phenotypically driven. Superbulls from the autumn spawning cohort were significantly older than the residual population, with added longevity potentially leading to spawning with the following cohort. A reduction in relative testis weight was apparent in superbulls, but spermatophore production remained high. Generalised additive mixed models indicated temperature, location and hatch year had significant effects on size-at-age. Weak correlations between warm El Niño–Southern Oscillation phases and superbull abundance were found. The results suggest that superbulls provide temporal connectivity and arise through phenotypic plasticity, likely providing connectivity as a side effect of body shape and size rather than a genetically selected advantage.

Discrete Spawning Aggregations of the Loliginid Squid Doryteuthis gahi Reveal Life-History Interactions of a Dwarf Morphotype at the Center of Its Distribution Range

“…Since a length-weight power function on adult specimens revealed a coefficient <3, these findings also support the dwarf morphotype hypothesis, suggesting that a small reproductive morphotype is consistently occurring along the HCS between the two genetically different centers of abundance, the Chilean -Falklands/Malvinas and the Peruvian groups (Ibáñez and Poulin, 2014;McKeown et al, 2019). Similar morphological changes owing environmental variability have also been described in males D. gahi from the Patagonian shelf population (Jones et al, 2019) and also in the jumbo squid D. gigas from Peruvian waters (Argüelles et al, 2008b;Keyl et al, 2011;Arkhipkin et al, 2015a), enhancing the role of cephalopod plasticity when facing variable environmental conditions. Ongoing work on this Humboldt morphotype of D. gahi will complement population genetic studies as well as behavioral components associated to reproductive and trophic interactions in captive conditions.…”

Ontogenetic growth responses to the environmental changes of the swordtip squid (Uroteuthis edulis) spring stock in the East China Sea

“…Statolith growth increment width becomes wider with the increase in habitat temperature (within the suitable range) and feeding activities and is an important medium for revealing the individual's life history traits (Arkhipkin, 2005; Arkhipkin et al, 2018; Arkhipkin & Shcherbich, 2012; Jones et al, 2019). The hatching temperature of each monthly group (March group to May group) of the spring stock gradually increases and a small increase in hatching temperature in the embryonic stage can accelerate the individual hatching process, thus providing a suitable habitat environment for paralarvae at the same age (Pecl & Jackson, 2008; Wang et al, 2013; Yamaguchi et al, 2018).…”